I found few minutes to redraw my soldering station driver so I can send it to itead before I go to vacation :) ... software is still not done (the old one works but is not using encoder, not reading thermocouple properly etc etc ..)

Upgrades from v11. thermocouple is read properly. The circuit used to get the K-type to go 0-5V came from microchip's app note2. 3 buttons are replaced with rotary encoder with button3. DS18B20 is added to read ambient temperature (thermistor returns difference in temp between hot and cold join so you need to know temperature of the cold join to know what is the temp of the tip. I decided to go with DS18B20 because I just figured out I have 10+ of those in the drawer)

Future upgrades1. make nicer PCB (I make ugly pcb's... especially when dealing with slow speeds like here)2. there are some free pins that might be used for something ..

ONE SUPER IMPORTANT THING!!!SID do not have a FUSE on the power input. You MUST HAVE FUSE!!! I do not use fuse on PCB because all fuses I have are for "wires" so I have 2.5A glass fuse on the wire bringing 24 VAC into the PCB. BE SURE TO ADD THAT FUSE. 2.1-2.5 A is what you need depending on what type of LCD you use. The whole circuit (48W heater + everything on board + standard lcd) takes 2100 mA MAX. On top of that you need current for lcd back light. I have here LCD's that pull 30 mA and I have some that pull 280 mA for the back light, and I used some earlier that pull a whole amper!!! Anyhow whatever you do ADD A DARN FUSE TO THE POWER INPUT!!! DO NOT TURN ON SID WITHOUT IT!!

PCB's arrived from SEED. Not sure why but I was unable to locate "e-tested" ones. Half was taped with a paper so there definitely are 2 groups of pcb's but which ones are tested - beats me :D

Now, as usual the pcb's look great :) (taken into account that there is a lot of leave way in my design, I think this board is 10/10).

When I disassembled my old driver I found (idiot) that I have on the toroid a 6VAC output and 24VAC output and not only a single VAC output for everything so I will revise the PCB to be able to use this feature too. Anyhow I replaced the toroid with a single 12VAC one as 24VAC is too much for the 7805 (I actually use BT05T but same thing just bit better) and 24VAC is also too much for the pencil; it works but heats too fast too far :D

I assembled some quick firmware and - it works :)

The major issue I see with it is that k-type thermocouple is in the heater so the temperature of the tip is impossible to know with some significant accuracy + time it takes for heat to propagate from heater trough to the tip is significant unknown value :(

The driver actually works like a charm - if you take the "numbers" on display as some "arbitrary value" and not temperature in C :D. The tip temperature is held pretty good and it all works great, it's just that "values" are meaningless. The 500C heater temp is actually around 220C on the tip ... I'll see if there's anything to be done wrt that problem but most probably some "custom calibration" is the way to go.

Attached all files required to reproduce the controller. PCB/Schematic are made in PROTEUS (pdf files also available as is gerber), firmware in CSC PICC.

Redo the schematic / PCB in KiCad so to comply with the openness of the project (Proteus is great but is far from open, and AFAIK there's nothing free from Proteus, not even reader for Proteus schematic/pcb files, and if I'm redoing it to be open then KiCad is better solution then Eagle since Eagle is as closed as Proteus)

Allow for 2 AC inputs. One for the heater and other for the 5V logic (then you can always short them and power from single source if you want, but if you already have 2 outputs...)

ICSP connector so that it can be reprogrammed without dissasembling the device (getting the icsp connector on the front plate :D - I have a hole on the plate left over from a third button from old version that I might use for some connector with 5 pins for icsp)

240 gain requires 24K resistors there, not really available easy (I checked mu drawers, contacted my supplier and seems that 24k I need to order & wait 2 weeks to get it - same price as all the other but for some reason they don't have it around) so adding 3 footprints instead of just one would be great (attm I soldered 22k + 1k + 1k (look at picture attached, it is 2x1206+0804 on top :D it works but .. )

I have zero idea why I used some resistors on the pcb as trough hole and some as smd :D but new version should use 0804 only. I do not have good source for smd potentiometers but the lcd contrast pot should also go smd, no reason for a big trimmer there when it is a "set and forget" thing anyway.. The cap's should go smd too (except for the 1000uF ones, those I'd keep trough hole as I have not found 1000uF smd tantalums cheap and I do not know how to solder the "can" smd electrolytes by hand)

firmware updates (proper firmware still required):

pid - (this initial version I made without pid as I don't know enough about this pencil attm. The temperature transfer function from heater to the tip is weird. Looks like the transfer takes a lot of time and with measurement on the heater making proper control on the tip is hard to achieve - maybe impossible)

240 gain requires 24K resistors there, not really available easy (I checked mu drawers, contacted my supplier and seems that 24k I need to order & wait 2 weeks to get it - same price as all the other but for some reason they don't have it around) so adding 3 footprints instead of just one would be great (attm I soldered 22k + 1k + 1k (look at picture attached, it is 2x1206+0804 on top :D it works but .. )

hm, I'm getting fast in KiCad but it seriously misses some required options like "export to PDF" for example :( ... and middle mouse for panning is also ...

anyhow, if anyone want schematic in KiCad, here it is. There's no PCB made for it (if you make one please share) as I seriously hate the sch->pcb process in KiCad so will not be using it to make PCB (not ever unless they seriously change something in the flow)

Now I just need to find a source of this "pencils". There is a huge "open market" (mixture of flee market and regular stores but all on big open field) near Belgrade and some Bulgarians and Romanians are selling these pencils. They have no markings on them but are same construction as hakko 907 esd handle, take same tips (I purchase original hakko tips and use with my irons)... They work 24VAC 1.7A so 40W. The "QUICK 907A" handle I have on my main soldering station (analog) is 50W one so similar, also hakko knockoff...

Anyhow I will give these boards to my friends as I really needed only one. Thing is I really should make double AC input as sending 24VAC to 7805 or BA05T or any other 3pin regulator ain't gonna work properly. Not sure if removing 3 diodes and using only D3 while shortening D2 would help. It will be much more ripple but maybe regulator would have it easier :D ....

tayken wrote:By the way, the taped ones are e-tested ones. They should have a mark on the side.

hm well the one I used is from the "untaped" bunch :D works like a charm :D i see a small marking on a side, looks like graphite pen or something else very thin. This is the first batch from seed I did, I used ITead so far and they always came marked with a thick red marker on a side :D, not that it matters :D (I switched to seed for pcb's as seed allows payment with ccard compared to itead that only allows paypal).

This temperature readout is messing with my head so I decided to do some testing. I attached real K-type probe to the sensor input and heated/cooled water with sensor in (and another commercial temperature monitor in same water) and this rig show 0.2C accurate results from 30C to 90C (have not tested outside that range).

Now I removed the metal parts of the iron and submerged the ceramic heater in the hot water (60C) and the readout show values from 115 all up to 200C .. so it definitely seems that inside this heater is not K-type thermocouple as ppl online suggest. The sensor do generate some voltage but it is definetely not Ktype thermocouple. I do have another soldering iron that does have a thermocouple and that one behaves perfectly.

I found schematic for the HAKKO 936 (it uses same 907 pencil) and from what I can read they are using sensor in a feedback loop on the op-amp so they are definitely using this sensor as a NTC/PTC with few op-amps to linearize it. So my initial design (where I actually used that sensor as thermistor and not thermocouple) was correct. This board will work with k-type ok (and with j-type too) but for HAKKO pencil it's not the one you want to use it with